DESCRIPTION (Adapted from Applicant's Description): While researchers have searched for a relationship between the cognitive deficits and depression that are both common in multiple sclerosis (MS), numerous investigations have failed to find an association. This failure may stem from the multifaceted nature of depression. Measures of depression tap a spectrum of symptoms (e.g., dysphoric/depressed mood, somatic complaints), and some may be more relevant to cognition than others in neurological disorders such as MS. While apathy has been historically associated with depression, recent evidence indicates that apathy represents an important and distinct neuropsychiatric phenomenon in its own right. Researchers recently found that apathy played a key role in predicting cognitive dysfunction in a variety of neurological disorders (e.g., Parkinson's disease, progressive supranuclear palsy). In contrast, no link was found between cognitive impairment and dysphoric mood, a core feature of depression. While a relationship between apathy and cognitive impairment has been identified in over half a dozen neurological populations, it has not been adequately examined in MS. Apathy has been associated with neuroanatomical damage to regions that are often affected by the MS disease process (e.g., prefrontal cortex). In addition, apathy has been linked to neuropsychological deficits commonly found in MS (e.g., in working memory, executive functions). The proposed study will demonstrate how apathy, when separated from other factors traditionally associated with depression, can serve as a key marker of cognitive dysfunction in persons with MS. Subjects will consist of 80 MS patients. Apathy will be measured with the Apathy Evaluation Scale and the Apathy subscale of the Neuropsychiatric Inventory. Subjects will complete a battery of cognitive tasks focussed on executive functioning and working memory. It is hypothesized that apathy will correlate negatively with performance on tests of executive functioning and working memory, and that apathy will significantly add to the explanation of variance in such performance beyond that accounted for by other neuropsychiatric variables measuring depression, fatigue, pain, and sleep disturbance. Empirical support for the initial hypotheses will lay the foundation for further rehabilitative research designed to improve both apathy and cognitive functioning in persons with MS.